In the manufacture of golf balls defects, such as flow lines, excess cover material, weld marks, protrusions, gate marks, depressions, buffing lines, paint blots, stuck molding flash, blisters, and other foreign matter (i.e., dirt, particulate, etc.), can form on the surface of the golf balls for a variety of reasons. Golf balls having such defects can be aesthetically displeasing and may exhibit a loss in aerodynamic performance. As such, it is common practice within the golf ball industry to inspect, in some manner, the surface of the golf balls for defects prior to painting (if necessary), packaging, and shipping.
Conventionally, golf balls are inspected manually. But given the excessive number of golf balls produced in a year (e.g. Titleist®, the number one ball in golf, produces over 276 million golf balls per year), however, manual inspection of every golf ball is physically and logistically impossible and, additionally, is very subjective. Manufacturers have, therefore, attempted to automate the inspection process and incorporate the inspection somewhere in the golf ball manufacturing sequence. Automated golf ball surface inspection is difficult, however, because of a golf ball's unique surface topography—curved and dimpled.
A substitute for visual inspection that is commonly employed to automatically inspect the outer surface of a golf ball typically includes taking an optical image of the ball and processing the image by comparing it to a reference standard. When the object to be inspected is dimpled, such as a golf ball, the difficulties in detecting defects on the surface are greatly increased. Because dimples are distributed on a spherical surface, they can appear in the image as artifacts, such as ellipsoids having indefinite major and minor axes shadows. It is, therefore, important for a detection system to be able to detect the difference between a dimple and a defect on the curved, dimpled surface.
U.S. Pat. No. 6,031,933 discloses one such method for inspecting the outer surface of a golf ball. In the '933 patent, the outer surface of a golf ball is inspected for defects by illuminating the golf ball with a single light source, rotating the golf ball at a constant speed in one direction, and taking a series of line images of the ball surface with a line sensor camera along a line perpendicular to the rotational direction of the ball. The camera then delivers the one-dimensional line data to a computer that assembles it into a two-dimensional image, converts a brightness change in the two-dimensional image in the rotational direction of the ball into a variation per preset unit, and subjects the resulting variation data to binary processing on the basis of a threshold set between the variation associated with the dimple and the variation associated with any defects, thereby detecting whether or not defects are present. Effectively, a light threshold, based on the dynamic range of the line data, is determined—light levels darker than the threshold value are deemed a defect and light levels above the threshold value are deemed not a defect (i.e., a shadow or dark area, that does not match the intensity profile of a dimple, represents a defect).
The '933 patent, however, is limited in the ‘area’ of the surface that can be inspected. Because the surface of a golf ball is curved and light does not bend, as one moves away from the equator (or center of the illumination) of the ball, the golf ball surface itself begins to appear as a shadow in a collected line (or two-dimensional) image, limiting the effectiveness of the imaging method. Because of their varying and non-discriminating nature, surface defects, unfortunately, are not limited to specific areas of a golf ball. The method of the present invention provides a novel way to address this issue by adding a second illumination source having a different wavelength (or range of wavelengths) than the first illumination source, in combination with an array of pass filters and two-dimensional area imaging (versus line imaging).